THE BLOOD-PRESSURE RESPONSE TO INFUSIONS OF ANGIOTENSIN-II DURING NORMAL-PREGNANCY - RELATION TO PLASMA ANGIOTENSIN-II CONCENTRATION, SERUM PROGESTERONE LEVEL, AND MEAN PLATELET VOLUME

OBJECTIVE: This study is a survey of the determinants of refractoriness to the pressor effects of angiotensin II during normal pregnancy. STUDY DESIGN: In 25 normal pregnant women, the effective angiotensin II pressor dose was determined 88 times from the twenty-fifth to the thirty-second week of gestation. Immediately before the angiotensin II infusion, blood samples were collected and measured for plasma angiotensin II concentration, serum progesterone level, platelet count, and mean platelet volume. RESULTS: The effective pressor dose had a significantly positive correlation with plasma angiotensin II concentration and serum progesterone level and a negative correlation with mean platelet volume. CONCLUSION: The pregnancy-associated refractoriness to angiotensin II is physiologically determined, at least in part, by the elevated circulating levels of endogenously produced angiotensin II and by the progesterone produced by the placenta, whereas platelet activation attenuates the relative refractoriness during normal pregnancy.